1. Field of the Invention
The present invention relates to steering mechanisms for two-wheeled vehicles such as motorcycles, and more particularly to a steering system which continuously adjusts the angle of the front fork of the motorcycle.
2. Description of the Prior Art
The steering system for a motorcycle or bicycle generally consists of a shaft rotatably mountd to the front portion of the frame of the motorcycle or bicycle, which forks into left and right arms extending down to the axle of the front wheel. The handlebars are attached to the shaft such that a torque applied to them is transferred to the front wheel, thus turning the motorcycle.
Other steering systems are similarly designed, but have a shaft that is separate from, but connected to, the fork arms. This allows the attachment of a steering damper to the shaft. The shaft may have threading whereby the user may adjust the effective length of the fork arms, or the arms may themselves be telescopic. The fork may also be provided with springs or other types of shock absorbers.
As is known by one skilled in the art, the characteristics and stability of the motorcycle depend to a great extent on the pitch angle of the front fork. Moreover, it is desirous to have the capability of adjusting this pitch angle. British Pat. No. 570,439, issued to Ballamy and Sheepshanks, describes one such method of adjustment. That patent discloses a plate which may be used to adjust the relative distance between the upper portion of the shaft and the upper portion of the fork, the lower portions of each remaining fixed. Adjustment of the plate requires loosening various bolts and washers, realigning the fork with respect to the shaft, and then retightening the bolts and washers. This invention is directed to adjusting the pitch angle to suit prevailing riding conditions.
Another steering system concerned with the front fork angle is U.S. Pat. No. 3,866,946, issued to Robison. The steering head disclosed by Robison also has a shaft coupled to the fork to allow variation in the pitch angle. This is accomplished by means of eccentric bearings mounted on each end of the shaft. Adjustment of the pitch angle requires removal of the end pieces of the head tube and changing the orientation of the bearings. Only four different settings are possible.
As one skilled in the art can appreciate, each of the aforesaid devices is difficult to adjust as they require the use of special tools, and the variability of the shaft angle is limited to discrete settings. Moreover, variation of the pitch angle is additionally useful during the actual turning operation of the vehicle. The motorcycle would have increased turning ability in turns if the pitch of the front fork was closer to the vertical. This is especially critical in dirt bike racing. The above inventions only allow adjustment when the motorcycle is idle and not being used. It would therefore be desirable and advantageous to devise a variable angle steering system which continuously varies the pitch angle of the front fork of a motorcycle as the front wheel is turned.